Within the field of shoulder prostheses, it is known, for example from FR-A-2 841 768, to use an intermediary component having two convex articulation surfaces designed to co-operate with a concave articulation surface belonging to the humeral component of the prosthesis and a concave glenoid articulation surface respectively. This type of prosthesis gives overall satisfaction, particularly since the distribution of the instantaneous centres of rotation of the articular surfaces in contact enables the point of application of the effort exerted by the deltoid during the abduction movement to be externalised. However, in some implantation configurations, the external part of the humeral component or the humerus risks coming into contact with the acromion, which may be irritating, or even painful, for the patient.
Similar problems may arise with a shoulder prosthesis that has a humeral component with a convex articulation surface, the intermediate component thus having a corresponding concave articulation surface. Problems of the same type may arise with a known hip prosthesis.
These are the drawbacks that the invention more particularly aims to remedy by proposing a new shoulder prosthesis in which the abduction effort exerted by the deltoid can be optimised, without risking interaction between the humerus or humeral component and the acromion at the end of the abduction movement. The invention also proposes a hip prosthesis.